1. Field of the Invention
The present invention relates to an apparatus and method for fabricating integrated circuits, and more particularly, to an apparatus and method for chemical mechanical polishing integrated circuit wafers.
2. Description of the Prior Art
Chemical mechanical polishing is used in the semiconductor industry to fabricate integrated circuit wafers for higher degree of planarity and uniformity. Chemical mechanical polishing typically involves the removal of an oxide or tungsten layer from the surface of a wafer such that peaks and valleys are removed from the wafer surface. The removal process utilizes an abrasive slurry suspending in an alkaline or acidic solution to planarize the surface of the wafer through a combination of mechanical and chemical action.
FIGS. 1A and 1B are schematic diagrams showing a conventional chemical mechanical polishing machine. The chemical mechanical polishing machine comprises a polishing platen 10 on which a polishing pad 12 is layered, a polishing head 14 for holding a semiconductor wafer 16 in position, and an injector 18 for applying a mass of slurry to the semiconductor wafer 16 during the chemical mechanical polishing process. In use, the polishing platen 10 is rotated and an abrasive slurry is sprayed onto the polishing pad 12 of the polishing platen 10. Once the slurry has been applied to the polishing pad 12, the rotating polishing head 14 moves downward to press the semiconductor wafer 16 against the polishing pad 12. As the semiconductor wafer 16 is pressed against the polishing pad 12, the surface of the semiconductor wafer 16 is mechanically and chemically polished.
The slurry is very important for the chemical mechanical polishing process. The improper operating properties of the slurry result in a fatal influence for the chemical mechanical polishing process. The slurry flow rate is especially important for the chemical mechanical polishing process. It is a key factor for the chemical mechanical polishing process to select a proper flow rate of the slurry and in-situ monitoring the flow rate during the chemical mechanical polishing process to ensure the flow rate of the slurry is under control.
However, for the conventional chemical mechanical polishing machine, a flow rate meter is usually disposed between the slurry pipes for monitoring the flow rate of the slurry during the chemical mechanical polishing process. The problems with the slurry flow rate, for example, slurry leakage, broken pipes etc, sometimes occurr after passing through the flow rate meter. As a result, the slurry flow is not supplied unto the polishing pad 12. This situation is not detected by the flowrate meter.
Accordingly, it is an intention to provide an apparatus and method for in-situ monitoring slurry flow rate during a chemical mechanical polishing process, which can overcome the above drawback encountered in the conventional chemical mechanical polishing machine.
It is an objective of the present invention to provide a system for in-situ monitoring slurry flow rate during a chemical mechanical polishing process, which can in-situ monitor a flow rate of slurry at a predetermined position approximating to an outlet of a slurry supplier during a chemical mechanical polishing process, so as to ensure flow of the slurry all through the chemical mechanical polishing process.
It is another objective of the present invention to provide a system for in-situ monitoring slurry flow rate during a chemical mechanical polishing process, which combines a chemical mechanical polishing apparatus with an impact pressure measuring device, and a flow rate of slurry supplied unto the chemical mechanical polishing apparatus which is controlled and adjusted according to impact pressure measured by the impact pressure measuring device, generated by the flow rate of the slurry.
It is a further objective of the present invention to provide a system for in-situ monitoring slurry flow rate during a chemical mechanical polishing process, which positions an impact pressure measuring device on a surface of a polishing platen so as to facilitate a polishing pad adhering unto the polishing platen. It is still a further objective of the present invention to provide a method for in-situ monitoring slurry flow rate during a chemical mechanical polishing process, which can in-situ monitor a flow rate of slurry during a chemical mechanical polishing process, and accordingly controlling and adjusting the flow rate of the slurry.
In order to achieve the above objectives, the present invention provides a system and method for in-situ monitoring slurry flow rate during a chemical mechanical polishing process. The present system comprises a chemical mechanical polishing apparatus with an impact pressure measuring device, circuit means for converting impact pressure to a flow rate, means for controlling a flow rate and slurry supply means. The impact pressure measuring device serves in-situ monitoring of the impact pressure generated by slurry flowing through and then supplied unto the chemical mechanical polishing apparatus during a chemical mechanical polishing process. Circuit means for converting impact pressure to a flow rate that serves the converting of the impact pressure to the flow rate of the slurry. When the flow rate of the slurry is equal to or over a predetermined flow rate of the slurry, circuit means for converting impact pressure to a flow rate provides a first control signal to means for controlling a flow rate to control the slurry supply means, adjusting the flow rate of the slurry supplied to the chemical mechanical polishing apparatus. When the flow rate of the slurry is less than the predetermined flow rate of the slurry, circuit means for converting impact pressure to a flow rate provides a second control signal for interrupting the chemical mechanical polishing process and triggering an alarm. The impact pressure measuring device is disposed in a predetermined position approximating to a polishing platen of the chemical mechanical polishing apparatus and corresponding with an outlet of slurry supply means. Thus, the flow rate of the slurry can be monitored at the outlet of slurry supply means and the flow of the slurry all through the chemical mechanical polishing process is ensured.